METTL3 depletion contributes to tumour progression and drug resistance via N6 methyladenosine-dependent mechanism in HR+HER2—breast cancer

Background Chemotherapy is an important strategy for the treatment of hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+HER2−) breast cancer (BC), but this subtype has a low response rate to chemotherapy. Growing evidence indicates that N 6 -methyladenosine (m 6 A) is the most common RNA modification in eukaryotic cells and that methyltransferase-like 3 (METTL3) participates in tumour progression in several cancer types. Therefore, exploring the function of METTL3 in HR+HER2− BC initiation and development is still important. Methods mRNA and protein expression levels were analysed by quantitative real-time polymerase chain reaction and western blotting, respectively. Cell proliferation was detected by CCK-8 and colony formation assays. Cell cycle progression was assessed by flow cytometry. Cell migration and invasion were analysed by wound healing assays and transwell assays, respectively, and apoptosis was analysed by TUNEL assays. Finally, m 6 A modification was analysed by methylated RNA immunoprecipitation. Results Chemotherapy-induced downregulation of the m 6 A modification is regulated by METTL3 depletion in HR+HER2− BC. METTL3 knockdown in MCF-7/T47D cells decreased the drug sensitivity of HR+HER2− BC cells by promoting tumour proliferation and migration and inhibiting apoptosis. Mechanistically, CDKN1A is a downstream target of METTL3 that activates the AKT pathway and promotes epithelial-mesenchymal transformation (EMT). Moreover, a decrease in BAX expression was observed when m 6 A modification was inhibited with METTL3 knockdown, and apoptosis was inhibited by the reduction of caspase-3/-9/-8. Conclusion METTL3 depletion promotes the proliferation and migration and decreases the drug sensitivity of HR+HER2− BC via regulation of the CDKN1A/EMT and m 6 A-BAX/caspase-9/-3/-8 signalling pathways, which suggests METTL3 played a tumour-suppressor role and it could be a potential biomarker for predicting the prognosis of patients with HR+HER2− BC.